1. Field of the Invention
This invention is related to surgical instruments that are used in insuflation procedures. More particularly, this invention is related to the use of verres needles to inject a gas into a body cavity to facilitate endoscopic surgery.
2. Description of the Prior Art
Prior to performing an endoscopic procedure in a body cavity, such as the abdomen, it is necessary to insufflate the body cavity in order to separate the wall of the cavity from internal organs and to create space between the organs. This separation creates space within which a surgical procedure may be performed by the use of endoscopic instruments, such as laparoscopy instruments for abdominal surgery. The insufflation procedure typically involves insertion of a pneuomoneedle or verres pneumoneedle into the body cavity, after which a gas, such as carbon dioxide gas, at a pressure in excess of atmospheric is injected through the needle to inflate the body cavity. After the body cavity has been sufficiently inflated, the verres needle is removed and replaced by a larger diameter trocar to allow the introduction of surgical instruments without allowing gas to escape.
Prior art verres needles are typically used to create the initial incision in the body cavity wall. These prior art verres needles typically include a tubular outer sheath having an outer diameter of approximately 2.1 mm. This tubular sheath is fabricated of metal and the exposed or distal end of the tubular sheath includes a cutting edge of surface for effecting the initial incision. Since this cutting edge could cut or nick internal organs if it remained exposed, prior art verres needles typically include a spring loaded stylet having a relatively blunt leading end. This stylet includes an inner projection that extends through the tubular sheath with the blunt end located adjacent to the sharp cutting edge of the tubular sheath. A spring is located at the trailing end of the stylet and is located between the stylet and the body of the outer sheath. The spring normally urges the stylet beyond the exposed cutting edge of the outer sheath so that the cutting edge is not in a position to create an incision or to inadvertently cut or damage an internal organ or blood vessel when the style is in its extended position. However, when the blunt end of the stylet engages a surface, such as a body cavity wall that can exert a force on the stylet, the coil spring in the verres needle subassembly is compressed, retracting the stylet blunt end and exposing the cutting edge. After the cutting edge makes the initial incision in the body cavity wall, the force on the blunt end of the stylet is removed and the spring urges the stylet back into its extended position so that the cutting edge is again sheathed by the blunt end of the stylet.
After the initial incision is made by the verres needle, higher pressure gas is injected into the body cavity through the verres needle. The outer sheath of prior art verres needles are hollow and the leading end, which protrudes into the body cavity is open. Two types of stylets are used in conventional verres pneumoneedles. The inner projection of the first type is hollow and either is open on the blunt leading end or has a side opening passage adjacent the blunt leading end. In either case, air can pass through the inner bore of the stylet and out the exposed end of the verres needle into the body cavity. The other stylet consists of a solid inner projection having an outer diameter that is less than the inner diameter of the outer sheath. A gap between the periphery of the inner projection and the inner peripheral wall of the outer sheath permits the passage of gas through the outer sheath. This type verres needle normally has an enlarged tip that protrudes beyond the leading end of the outer sheath in the extended position. When the blunt tip is forced back into the sheath to expose the sheath cutting edge, the enlarged tip may close off the bore of the outer sheath. In the extended position, gas can escape between the open end of the outer sheath and the blunt stylet tip. In either type of conventional verres pneumoneedle, the cross sectional area within the outer sheath is significantly less than the inner diameter of the bore of the outer sheath. Therefore the mass flow rate of gas through the verres needle is restricted by this reduced cross sectional area. Since the time needed to insufflate a body cavity is proportional to the flow rate through the pneumoneedle, this restricted flow rate means that this procedure will take longer than for a higher flow rate. For conventional verres pneuoneedles, the the elapsed time for this procedure can be on the order of five (5) min. during which time the entire surgical staff must wait before performing other procedures. If this procedure required less time, the operation could be more efficiently performed because the surgical staff and the surgical facilities could be more efficiently employed. A reduction is the time needed to perform the entire operation could also reduce the stress on the patient.